LONDON/DETROIT (Reuters) - The growing risk of a significant radiation leak at two Japanese nuclear power plants following Friday's earthquake and tsunami threatens to hurt an industry that has enjoyed a rebirth since the Three Mile Island accident in 1979 and the Chernobyl disaster in 1986.

On Friday, nuclear power advocates and environmentalists staked out familiar ground over the incident. But a wider public debate may be ignited if a major radiation leak occurs in Japan, said Paul Patterson, an energy analyst with consultants Glenrock Associates in New York.

That debate has been largely muted since the 1980s when rock concerts were held to galvanize opposition to nuclear power after the Three Mile Island incident in Pennsylvania and the popular movie "The China Syndrome," that raised awareness of the dangers of a nuclear reactor meltdown.

"The severity of what happens is what is important," Patterson said of the impact of the Japanese incident.

If there is a substantial radioactive release, there could even be questions about whether it could travel on the Pacific jet stream to the U.S. West Coast.

"It is serious and it could lead to a meltdown," said Mark Hibbs, a nuclear expert at the Carnegie Endowment for International Peace. "And what we're seeing, barring any information from the Japanese that they have it under control, is that we're headed in that direction."

But Naoto Sekimura of the University of Tokyo, said that a major radioactive disaster was not likely.

An 8.9-magnitude earthquake centered in northern Japan triggered a series of events at two Tokyo Electric Power Co plants that created conditions for a radioactive leak because there wasn't electric power to circulate cooling water over superheated uranium fuel rods.

The two TEPCO plants, the Daiichi plant and the Daini plant are around 40 miles (60 kilometers) from the epicenter of the earthquake that led to a tsunami and probably killed more than 1,000.

Nuclear industry advocates on Friday were saying that the ability of the nuclear reactors in Japan to largely withstand the power of the earthquake shows how safe nuclear power is.

But that was before a series of scary announcements from TEPCO that it had lost the ability to control pressure at several reactors and that it was having trouble with a valve that would allow reactor pressure to be eased.

Thousands of residents were evacuated from the immediate area of the Fukushima plants, about 150 miles 240 km (240 kilometers) north of Tokyo.

Industry experts said the precautions taken at Fukushima showed that enhanced security at nuclear power plants should prevent any disaster. But green groups said the threatened leak showed that the risks were still too high.

"I wouldn't expect there to be a radiation emergency ultimately, they may have something to fix but it's a precaution more than anything else," said Sue Ion, former chief technology officer at British Nuclear Fuels, after Japan declared an atomic power emergency.

Altogether, some 11 Japanese reactors shut down after the earthquake. Successive layers of security should prevent any leak of radiation, said Jeremy Gordon, an analyst at the World Nuclear Association based in London.

NUCLEAR POWER GAINS RECENTLY

"The reactor designs that are up for consideration today are generation three where the safety systems operate at an even higher level," said WNA analyst Jonathan Cobb.

But environmental groups said the threat of a radiation leak underscored the general risks from atomic energy.

"We've opposed nuclear power for decades, and this is another proof that it can't be safe," said Sven Teske, director of renewable energy at Greenpeace International.

A leading U.S. scientist group said the incident highlighted the grave risk of inadequate back-up power to cooling systems at U.S. facilities.

New interest from governments and investors in nuclear power follows the development of more advanced plants, and a new focus on security of energy supply and moves to reduce carbon emissions. Nuclear plants generate low-carbon power in contrast to fossil fuels and can produce constantly unlike wind and some other clean energy sources.

The Vienna-based International Atomic Energy Agency (IAEA) estimated last month that about 10 countries have decided to introduce nuclear power and started preparatory infrastructure work, up from four in 2008.

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